Tone control for radio-phonograph combination



Nov. 12, 1957 G. E. OWEN, JR, ETAL TONE CONTROL FOR RADIO-PHONOGRAPH COMBINATION Filed Feb. 23, 1954 RESPONSE RESPONSE INVENTORS George E Owen Jz BY file/lard J Harasek.

REGE XKGQQRQ United States Patent 2,813,155 ToNE CONTROL FOR RADIO-PHONOGRAPH COMBINATION George E. Owen, Jr., Melrose Park, and Richard Harasek, Chicago, Ill., assignors to Motorola, Inc., Chlcago, 111., a corporation of Illinois Application February 23, 1954, Serial No. 411,850 6 Claims. (Cl. 179100.11)

The present invention relates generally to radio phonograph combinations and more particularly to an improved tone control for use in such devices.

A-common method of controlling the tone or audio frequency response range of an electronic audio system is to provide a variable control means for by-passing selected portions of the higher frequency signal components translated by the system, so that these components are attenuated in the reproduced sound. This is often accomplished by use of a capacitor and variable resistor connected between a point where the signal components appear and a point of reference potential, or ground. It is also feasible to utilize the same variable control means to increase the level of the lower frequency audio components, for example, by decreasing the attenuation thereof, as more of the high frequency components are bypassed thereby producing a pronounced variable tonal eifect by operationof the one control.

In the pending application of William Blinoif, et al., Serial No. 350,022, filed April 21, 1953, which relates to radio phonograph combinations, a tone control similar to the type just mentioned is shown incorporated in an audio stage of the system. That application describes a superh'eterodyne radio receiver with provision for phonograph record reproduction by causing a tone arm to modulate a fixed signal from the heterodyne oscillator, with this modulated signal then being translated through the receiver in much the same manner as would a received radio signal. Since the intermediate frequency amplifier, the detector and the audio stages are used in both radio reception and in record reproduction, the tone control incorporated in the audio stage may suffice for both types of operation.

However, it has been found that the audio signals produced by certain phonograph tone arms usually contain strong bass or low frequency audio components as compared with a regular broadcast signal passing through the receiver, which usually contains somewhat attenuated treble and bass components with enhanced middle tones. It is therefore apparent that the type of tone control described above is incapable of affording the most desirable range of tone control for both phonograph and radio reproduction.

It is, accordingly, an object of the present invention to provide an improved and simplified tone control for use in a radio phonograph combination system which produces a desirable tonal range when the unit is operated either as a phonograph player or as a radio receiver.

A further object of the invention is to provide a single variable control for selecting the tonal reproduction range in a radio phonograph combination, which control may be operated to select the more desired frequency response for either radio or phonograph operation.

A feature of the invention is the provision of a tone control for a combination radio phonograph in which record reproduction is accomplished by modulating an oscillator signal and feeding .the signal through a tuned amplifier, a detector and an audio unit with the tone control for record reproduction including means to detune the oscillator frequency to attenuate a portion of the modulated signal in the tuning means of the amplifier.

Still another feature of the invention is the provision of a single tone control means which may be selectably switched to provide desired tonal response in an electronic unit functioning either as a radio receiver or as a phonograph record player.

Further objects, features and the attending advantages of the invention will be apparent upon consideration of the following description when taken in connection with the accompanying drawing in which:

Fig. 1 is a wiring diagram of a radio-phonograph incorporating the improved tone control of the invention; and

Figs. 2 and 3 are curves useful in understanding the operation of the invention.

in practicing the invention there is provided a tone control for a combination radiophonograph in which phonograph record playing is effected through modulation of a local oscillator radio frequency signal in accordance with recorded intelligence after which this signal is then translated through regular channels of the receiver including the tuned intermediate frequency amplifier, the second detector, and the audio system. A single control means is used during regular broadcast reception to control tone, or frequency response, in this instance by varying the amplitude of the lower audio frequency components or through by-passing a portion of the higher audio frequency components. During record playing this same control is switched to make connection with a capacitor in the local oscillator signal determining network thus allowing variation of the frequency of this signal. The variation detunes the modulated signal so that attenuation of a portion of the signal is obtained as it passes through the tuned intermediate frequency amplifier. A portion of the control may remain connected to the audio section during record playing to allow shunting of certain audio frequency compo nents in addition to oscillator detuning thus providing a more effective regulation of frequency response.

The receiver shown in Fig. 1 is similar to that described in the copending application mentioned previously herein, and it includes a loop antenna 10 and a variable tuning capacitor 11 connected across having one side connected to a point of reference potential or ground which is usually the chassis of the receiver. The other side of capacitor 11 is coupled through a capacitor 14 to the control electrode 12 of an electron discharge device 13 which may be a standard converter valve. Control electrode 12 is also connected to the automatic gain control (AGC) lead grid lead resistor 16.

Discharge device 13 has a cathode 17 connected to B through an inductance coil 18, and the device has a further control electrode 19 which is connected to cathode 17 through grid-leak resistor 20. Control electrode 19 is also connected to a coil 21 which is capacitively coupled to coil 23. Device 13 includes a screen electrode 22 which is connected to B+. Electrodes 17, 18 and 22 of discharge device 13 constitute the heterodyne oscillator section of the device and, to complete the oscillator circuit, a resonant network is provided including an inductance coil 23 shunted by a variable capacitor 24 when switch S1 is in the R position for radio reproduction. Inductance coils 18 and 23 are inductively coupled one to the other and, as previously noted, coil 21 is capacitively coupled to coil 23. For phonograph reproduction, switch S1 is placed in the P position to connect a capacitor 25 and trimmer 26 across coil 23 and to connect capacitor position of S3. Capacitors 27 from the coil 23 to the P the antenna circuit and 15 of the receiver through 25, 26 and 27 cause the oscillator to be tuned substantially to the intermediate frequency of the receiver.

Discharge device 13 has an anode element 28 connected to B+ through the primary winding 29 of an intermediate fr quency transformer 30. Winding 29 is also connected through blocking capacitor 34 to capacitor pickup 36, and the other connection of pickup 36 is joined to the P position of S2. The R position of S2 is connected to the input of intermediate frequency amplifier 37 and to the junction of capacitors 38 and 39. In the P position of S2 capacitor 34 and pickup 36 are connected from the primary 29 of transformer 30 to the secondary 41 while in the R position, 38 is shorted out so that capacitor 39 tunes coil 41. AGC line is also connected to the intermediate frequency amplifier 37 in well known manner.

The output terminals of amplifier 37 are connected across the primary winding 51 of an intermediate transformer St) and across a capacitor 52, the secondary winding 53 of the transformer being shunted by a capacitor 54 andthe transformer 50 then constitutes band pass network through the tuned circuits formed therewith. One side of the secondary winding 53 is connected to the anode element 56 of a discharge device 57 while the other side of winding 53 is connected through filter capacitor 59 to the cathode element 60 of device 57 and through load resistor 62 to B. Discharge device 57 is shown as a diode-triode electron valve. Resistor 62 is shunted by a series connection of capacitor 63 and variable resistor 64, and resistor 62 is also connected to AGC line 15 through a resistor 66. A variable arm of resistor 64 is connected to a control element 66 of discharge device 57 through a coupling capacitor 67, and a resistor 69 connects the control element 66 to B. The anode 70 associated with control element 66 is connected to B+ through a resistor 72 and to the input terminals of audio amplifier 73 through coupling capacitor 74. A bypass capacitor 76 couples anode 70 to B, and a capacitor 77 couples B- to the frame or chassis of the unit.

In the Rposition of S3, a bypass capacitor 80 is connected from anode element 70, which is a point where the audio signal appears with respect to B, to one side of a variable resistor 81. In the P position of S3 this side of resistor 81 is connected to capacitor 27. A taplpoint on variable resistor 64 is connected to the other side of resistor 81 througha resistor 83, and that side of resistor 81 is by-passed to B through a capacitor 85.

The output terminals of audio amplifier 73 are connected to the primary winding of output transformer 90, while the secondary winding of transformer 90 is connected'to an audio reproducer 91.

Operation ofthe unit as a radio receiver is similar to that of known receivers and occurs when S1, S2 and 83 are in the R position. A signal impressed on loop antenna 10 is tuned by the loop and capacitor 11 and passed to control element 12. An oscillator signal, the frequency of which is determined by coil 23 and capacitor 24, is used to heterodyne the signal on element 12 to produce an intermediate frequency signal. This signal is selected in transformers 30 and 50 and amplified in amplifier 37. Demodulation occurs through elements 56 and 60 of discharge device 57, with the resulting audio signals appearing across resistor 64 where they are tapped off and passed to control element 66. Audio amplification takes place in device 57 and the signal is coupled to amplifier 73 and from there to the sound reproducer 91.

Tone control is effected for radio reception through variation of variable resistor 81. When the contact arm of 81 is near the end connected to capacitor 80 a comparatively large portion of the treble or high audio frequency components is by-passed to B. A fixed portion of the high audio frequency components is by-passed to B- through capacitor 85 so that by placing the contact arm of 81 near the end of 81 connected to resistor 83, a portion of the bass or lower audio frequency components 4 is shunted to B. Thus the two effects are opposite and occur at opposite positions of the arm on resistance 81 so that a great range of audio frequency response may be had through operation of only one control.

S1, S2 and S3 may be ganged to facilitate preparing the unit for record playing which takes place in the P position of these switches. It may be seen that tuning of the oscillator to substantially the frequency to which the transformers 30 and 50 are tuned will produce a signal that can be modulated by recorded intelligence and translated through the receiver in much the same manner as would a received broadcast signal. As explained more fully in the pending application above mentioned, capacitors 25 and 26 tune the oscillator substantially to the intermediate frequency and this signal is modulated by the pick-up or tone arm 36 by variation of the coupling across transformer 30.

In accordance with the present invention capacitor 27 is switched to be connected to resistor 81 when S3 is in the P position, so that variation of resistor 81 will cause a variation of the frequency of the signal generated by the oscillator. The portion of resistor 81 connected to shunt portions of the bass in the audio signal may remain connected .to perform its formerly described function. The effect of the detuning of the local oscillator may be understood by reference to Figs. 2 and 3.

The curve shows the asymetrical frequency response of the transformers 30 and 50 with the resonant frequency of i The frequency of the oscillator signal is represented as f, the upper modulation sideband as F1 through 1 and the lower modulation iside band as 1, through f and it may be seen that the high frequencies of the modulating signal will be attenuated in passing through the transformers. The lower or bass components of the signal, in the area near or f,, will pass with the greatest amplitude. As previously mentioned a signal produced by certain phonograph tone arms often contains strong'bass tones with the middle and treble tones being somewhat attenuated so that the final result would be sound reproduced with an undesirable amount of bass tones on two counts, the nature of the signal from the tone arm and the treble attenuation in the transformers.

Assuming the lower sideband will be demodulated, a shift of 1 equal to 3 or 4 kc. to the high frequency side of f0, would position the bass frequencies so that they are attenuated, while the treble frequencies are positioned to pass through the transformers with less attenuation than 'without the shift of f. Fig. 3 shows this situation and it is apparent that the desired attenuation of the bass is possible through detuning of the oscillator signal. With the asymmetrical response of the transformers as shown, a less gradual, and therefore more pronounced, change in the low frequency response is possible with variation in f.

To use the bass amplitude control already connected to one side of resistor 81 and at the same time to aid its effect with oscillator detuning, trimmer 26 is adjusted so that )o coincides with f when the arm of resistor 81 is'in a position to connect capacitor 27 directly to B. Then the bass is strong and the treble is comparatively weak in the resulting audio signal. However when the arm of 81 is moved to short-circuit capacitor 85, f is raised so that the bass is attenuated as in Fig. 3 and the bass is further reduced when the tone control is in this position as previously explained in connection with the radio tone control operation.

Thus it may be seen that a combination radio phonograph has been provided with a single tone control which may be used to allow the most desirable selection of audio frequency reproduction when used either as a radio or as a record player. By the simple addition of another section of the phono-re ceive'r switch and a capacitor in the local oscillator tuned circuit, the same control which allows selection of audio frequency response for broad= cast reception may be used to control a different and more desirable tonal range with attenuated bass for record playing.

While a particular embodiment of the invention has been shown and described, modifications may be made, and it is intended in the appended claims to cover all such modifications as fall within the true spirit and scope of the invention.

We claim:

1. In apparatus for selectively utilizing radio signals and phonograph signals, the combination of a local oscillator including a frequency determining network, switching means included in said frequency determining network for selectively causing said oscillator to generate a first signal of a selected frequency for phonograph reproduction and a second signal of a different frequency for radio reproduction, phonograph pickup means for modulating said first signal in accordance with recorded intelligence but with increased low frequency components, means for heterodyning received radio signals with said second signal to produce an intermediate frequency signal,

a utilization device, circuit means for translating the modulated first signal and the intermediate frequency signal to said utilization device, said circuit means including at least one band-pass network having a selected response characteristic and capable of providing selective attenuation of the modulation side bands of the modulated first signal, and a tone control circuit including capacitor means coupled to said frequency determining network of said local oscillator and variable resistor means coupled to said capacitor means for changing the frequency of said first signal to increase the attenuation of the low frequency modulation side bands of said modulated first signal by said band-pass network.

2. In a combination radio receiver and phonograph record player, the combination of a local oscillator including an electron discharge valve, a frequency determining network withtuned circuit means connected from said network to a point of reference potential, said tuned circuit means having a first tuning portion for establishing a first signal of a selected frequency for radio reception and a second tuning portion for establishing a second signal of a different frequency for phonograph record reproduction; switch means for selecting said first tuning portion and said second tuning portion of said frequency determining network; means for modulating said second signal in accordance with recorded intelligence to produce a modulated signal having an excess of certain frequency components; means for heterodyning received radio signals with said first signal to produce an intermediate frequency signal; circuit means for translating said modulated signal and said intermediate frequency signal, said circuit means including a selective portion with a bandpass network having a frequency response characteristic such that modulation side bands of translated signals may be attenuated therein; and a tone control circuit including capacitor means and variable resistor means series connected across said first tuning portion of said tuned circuit so that variation of said variable resistor means changes the frequency of said second signal to attenuate the aforementioned certain frequency components of said modulated signal in said band-pass network.

3. In a combination radio receiver and phonograph record player, the combination of a local oscillator including an electron discharge valve and a frequency determining network with tuned circuit means connected from a point in said network to a point of reference potential, said tuned circuit means having a first tuning portion for establishing a first signal of a selected frequency for radio reception and a second tuning portion for establishing a second signal of a different frequency for phonograph record reproduction; switch means for selecting said first tuning portion and said tuning second portion of said frequency determining network; means for modulating said second signal in accordance with recorded intelligence to produce a modulated signal;

means for heterodyning received radio signals with said first signal to produce an intermediate frequency signal; circuit means for translating said modulated signal and said intermediate frequency signal, said circuit means including a selective portion with a band-pass network having a frequency response characteristic such that modulation side bands of translated signals may be attenuated therein, a detector portion for demodulating said modulated signal to produce a demodulated signal and an audio portion for amplifying said demodulated signal; said audio portion having at least one signal point at which said demodulated signal may exist with respect to said point of reference potential; and a tone control circuit including by-pass capacitor means connected. to said signal point of said audio portion, oscillatorcapacitor means coupled to said point in said frequency determining network and resistor means with a point connected to said point of reference potential and a point switchably connected to said by-pass capacitor means for shunting selected portions of said demodulated signal and to said oscillator capacitor means for detuning said signal of a second frequency for attenuating selected portions of said modulated signal in said band-pass network.

4. In a combination radio receiver and phonograph record player, the combination of a local oscillator including an electron discharge valve and a frequency determining network with tuned circuit means connected from a point in said network to a point of reference potential, said tuned circuit having a first capacitor portion for establishing a first signal of a selected frequency for radio reception and a second capacitor portion for establishing a second signal of a different frequency for phonograph record reproduction; switch means for selecting said first capacitor portion and said second capacitor portion of said frequency determining network; means for modulating said second signal in accordance with recorded intelligence to produce a modulated signal; means for heterodyning received radio signals with said first signal to produce an intermediate frequency signal; translation circuit means for translating said modulated signal and said intermediate frequency signals, said circuit means including a filter portion with a band-pass network having a frequency response characteristic such that modulation side bands of translated signals may be attenuated therein, a detector portion for demodulating said modulated signal to produce a demodulated signal and an audio portion for amplifying said demodulated signal, said audio portion having a signal point at which said demodulated signal exists with respect to said point of reference potential and volume control means with a tap point thereon; and a tone control circuit including variable resistor means with slider means connected to said point of reference potential and first and second end terminals, first capacitor means connected to said point of reference potential and, with said first end terminal, to said tap point for shunting selected portions of said demodulated signal, second capacitor meansvconnected to said signal point and third capacitor means connected to said point in said network and switch means to connect said second end terminal of said resistor means to said second capacitor means for by-passing portions of said demodulated signal and to said third capacitor means for detuning said second signal to attenuate a portion of said modulated signal in said band-pass network.

5. A tone control system for signal translating apparatus including in combination, signal supply means for supplying a radio frequency signal amplitude modulated by an audio signal, said signal supply means including a radio frequency oscillator having a tuned circuit comprising impedance elements adapted to determine the frequency of said radio frequency signal, a band pass network of selected frequency response adapted to attenuate portions of the modulated radio frequency signal and to translate the modulated signal from said signal supply means, a detector for deriving the audio signal from said radio frequency signal, an audio circuit for translating the derived audio signal, said audio circuit having a selected audio frequency response, and variable resistor means included insaid audio circuit and adapted to vary the frequency response thereof, said variable resistor means being coupled to one of said impedance elements of said tuned circuit so that variation thereof shifts the frequency of said radio frequency signal to attenuate portions thereof in said band pass network simultaneously with variation of the frequency response in said audio circuit.

6,. A tone control system for signal translating apparatus including in combination, signal supply means for supplying a radio frequency signal amplitude modulated by an audio signal, said signal supply means including a radio frequency oscillator having a tuned circuit adapted to determine the frequency of said radio frequency signal, a band pass network of selected frequency response adapted to attenuate portions of the modulated radio frequency signal and to translate the modulated signal from said signal supply means, a detector for deriving the audio signal from said radio frequency signal, an audio circuit for translating the derived audio signal, byrpass capacitor means connected from said audio circuit to grbund fo b p ing c a P r n of a audio sis nal, an impedance element coupled to said tuned circuit of the radio frequency signal generator, and variable aresistor means coupled across "said by-pass capacitor means to shunt portions of said audio signal, said variable resistor means also being coupled to said impedance ele ment so that variation thereof shifts the frequency said radio frequency signal to attenuate modulated pore tions thereof in said band pass network simultaneously with shunting of said audio signal.

References Cited in the file of this patent UNITED STATES PATENTS 

